Palladium base alloy and method of producing same



United States Patent 3,137,571 PALLABIUM BASE ALLOY AND METHGB 0FPRCDUCING SAME Irving Cooper, Brookl N.Y., assignor to Joseph E. Cooper8; Sons Inc., New York, N.Y., a corporation of New York No Drawing.Filed Jan, 31, 1962, Ser. No. 170,223 8 Claims. (Ci. 75--1'72) Thisinvention relates to novel alloys of palladium and gallium, and to amethod for their production. More particularly, the invention concernspalladium base alloys containing from about /2% to about 15% by Weightof gallium.

Alloys of metals of the platinum group with baser metals have beenemployed commercially for many years in applications such as electricaland switch contacts, electrical conductors, resistance Wire, and thelike, where high electrical and thermal conductivity, resistance to heatand corrosion, ductility, and tensile strength are of importance. Thus,such metals as platinum, palladium, rhodium and iridium have beenalloyed with silver, nickel, copper and zinc. A known alloy of platinumcontaining about 8% tungsten is extensively used for the production ofelectronic components, for example as a wire contact member in diodes.This alloy has disadvantages which include a Rockwell hardness of onlyabout 22, and a fairly low resistance to flexing or bending, frequentlybreaking when first sharply bent. Alloys of palladium and zinc have beenproposed for telephone circuitry, but the preparation of these alloysoffers some difficulty in that it involves diffusion of the zinc intothe palladium at high temperatures.

In accordance with the present invention, new and useful alloys havebeen prepared from palladium and gallium which possess outstandingproperties of resilience, hardness and resistance to fatigue. Thesenovel alloys comprise palladium containing from about /2% to about 15%by weight of gallium.

The new alloys of the invention are useful as electrical contactelements, for example with silicon diodes. An alloy containing about /z%to 2 /z% and preferably about 1% to 2% gallium has proved especiallyuseful for diodes as a substitute forgold bonded diodes. They canreadily be manufactured in any form, shape or thickness, as for example,in the form of sheets or wires of any desired gauge. Their resiliencerenders them suitable for use for small springs for watches andscientific instruments. The resistivity of the alloys makes themespecially valuable in potentiometers.

The alloys of palladium and gallium are prepared simply and directly byheating together palladium metal in the form of strip or wire and therequired quantity of gallium metal at a temperature slightly above themelting point of the palladium until the molten mass has becomehomogeneous. The mass is allowed to cool and can be fabricated into anydesired shape. The novel alloys of the invention can be heat treated.

The starting materials are palladium, preferably of pure grade (99.9%),having a melting point about 1554 C., and a specific gravity of 12.0,and gallium metal. The gallium is a silvery-white metal, having amelting point of 29.7 C., and hence generally liquid at ordinarytemperatures, and having a boiling point of 1983 C. Its specific gravityis 5.9 (solid).

The palladium-gallium alloys of the invention have a silvery-whiteappearance, and a melting point slightly below that of palladium. Thespecific gravity is about 11.15.

3,137,571 Patented June 16, teen The preparation and properties of thenovel palladiumgalliurn alloys of the invention as a class areillustrated by one preferred embodiment of the invention, which is aribbon alloy of palladium containing 8% gallium by weight, and are setforth in the following example.

Example 92 grams of palladium wire were heated together with 8 gramsgallium in a crucible placed in an electric furnace until the palladiumhad completely melted, the temperature then being 2831 F., and the masshad become homogeneous. The molten alloy was allowed to cool, removedfrom the crucible, and formed into ribbon. If desired, the alloying canbe conducted under an atmosphere of an inert gas, such as nitrogen.

The resulting alloy was silvery-white in appearance, and had a specificgravity of 11.15. It possessed a tensile strength of about 200,000pounds per square inch, and a hardness on the Rockwell C scale of 36.

The alloy had an electrical resistance of 250 ohms per circular milfoot. It is very ductile and can readily be rolled into wire or flatribbon.

The electrical resistance properties of the alloys of the invention havebeen found to be a function of the amount of gallium present, higherpercentages of gallium imparting higher resistance and vice versa. Whenrolled into ribbon of widths ranging from 0.015 to 0.0700 inch andthickness ranging from 0.002 to 0.0095 inch, they provide an electricalcontact member which is especially effective and economical inconnection with diodes.

The following is data on the various percentages of gallium alloyed withpalladium.

Resistance,

Hardness ohms/c.m.f. 7

Pure Palladium 1R0ckwell B.

22-Rockwell B." 56Rockwell B. 4Rockwell O. 35Rockwel1 C. 45-Rockwell "0.

15% Gallium from about /2% to about 15% by weight of gallium, the

remainder of the alloy being palladium.

3. A palladium base alloy consisting essentially of from about /2% toabout 2 /2% by Weight of gallium, the remainder of the alloy beingpalladium.

4. A palladium base alloy consisting essentially of v 0 base alloyconsisting essentially of 98% to 99% palladium and 2% to 1% gallium byweight.

References Cited in the file of this patent Hansen: Constitution ofBinary Alloys, 1958, McGraw-, Hill Book Company, Inc., New York, page752.

1. A PALLADIUM BASE ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 1/2% TOABOUT 15% BY WEIGHT OF GALLIUM.